Effect of intravenous anesthetic drugs on fertilization rate in oocyte retrieval

embryo transfer (IVF-ET), can be performed to obtain viable oocytes from ovarian follicles before ovulation through needle retrieval [1]. As the needle punc-tures through the vaginal wall and explores the eggs in


Introduction
Transvaginal ultrasound-guided oocyte retrieval, a standard but invasive procedure in in vitro fertilization and embryo transfer (IVF-ET), can be performed to obtain viable oocytes from ovarian follicles before ovulation through needle retrieval [1].As the needle punctures through the vaginal wall and explores the eggs in follicular fluid.The accumulation of propofol in follicular fluid has the potential to impact oocyte fertilization and subsequently influence the quality of embryos.Previous animal studies [3,4] have indicated that propofol may have an impact on early embryonic development, although limited human studies [5] have been conducted.In light of these findings, we sought to investigate the potential effects of propofol exposure during pregnancy.
Therefore, we designed this retrospective cohort study involving subjects matched through PSM.This study attempts to explore the potential effects of intravenous anesthetic drugs on the IVF outcomes of subjects.

Methods
We retrospectively analyzed the clinical data of subjects who received oocyte retrieval in the Affiliated Hospital of Nantong University from January 2020 to December 2021.The inclusion criteria were as follows: (1) infertile females who received oocyte retrieval in IVF treatment; (2) follow-up data were complete.The exclusion criteria were as follows: (1) the subjects presented comorbidities, including hypertension, diabetes, liver diseases, kidney diseases, thyroid illness and autoimmune diseases; (2) the subjects showed oocyte cryopreservation and no oocyte cycles; (3) the subjects had taken other therapies after IVF.The study complies with the ethical guidelines of the Declaration of Helsinki and was approved by the Institutional Review Board of Affiliated Hospital of Nantong University (No: 2019-K039), and informed consent was obtained from all subjects.
The subjects were divided into the no-anesthesia group and the intravenous anesthesia group.In the no-anesthesia group, the oocyte retrieval was performed in the subject under a waking state.In the intravenous anesthesia group, the oocyte retrieval was performed in the subject falling asleep after anesthesia using intravenous propofol.Subject data including number of IVF cycles, ages of the couple, body mass index (BMI) of the female, duration of infertility, type of infertility (primary, secondary), infertility causes (tubal factor, ovulation disorders, endometriosis, premature ovarian insufficiency [POI], uterine factor, male factor, other causes and unexplained causes), ovarian stimulation protocols (A, B, C, D, E, F, G, H, I), basal follicle-stimulating hormone (FSH), basal luteinizing hormone (LH), basal estradiol (E2), basal antral follicle count (AFC), basal cancer antigen 125 (CA125), launch-day follicle-stimulating hormone (FSH), launch-day luteinizing hormone (LH), launch-day estradiol (E2), launch-day antral follicle count (AFC), trigger-day luteinizing hormone (LH), trigger-day estradiol (E2), trigger-day progesterone (P), the number of oocytes, the number of mature oocytes, fertilization way (IVF, intracytoplasmic Sperm Injection [ICSI], Half Intracytoplasmic Sperm Injection [HALF-ICSI]), anesthetic modality (no-anesthesia or intravenous anesthesia).The primary outcome was fertilization rate.In this study, fertilization rate was defined as the number of fertilized oocytes divided by the total number of retrieved oocytes.
In our center, ovarian stimulation was performed based on the female's age and ovarian reserve function.(A) The luteal phase long protocol: gonadotropin releasing hormone agonist (GnRH-a) was administrated in the luteal phase of the previous cycle; (B) The follicular phase long protocol: GnRH-a was administrated in the midluteal phase; (C) The ultra-long GnRH-a protocol: women received subcutaneous injections of long-acting GnRH-a for 2 to 4 months.(D) The ultra-short GnRH-a protocol: in this protocol, GnRH-a was used only once on day 2 of menstruation, after which gonadotropin (Gn) was initiated on day 3 and maintained until the administration of HCG.(E) The GnRH antagonist protocol: human menopausal gonadotropin (HMG) was administered daily from menstrual cycle day 3, and GnRH antagonist (0.25 mg/ day) was added from stimulation day 6.(F) The progestin-primed ovarian stimulation (PPOS) protocol: hMG at 150-225 IU and medroxyprogesterone acetate (MPA) at 10 mg were administered daily from cycle day 3. (G) The micro-stimulation protocol: clomiphene was given orally from days 2 to 3 of the menstrual cycle.(H) The natural cycle protocol: no ovulation-inducing medication was given.(I) The other protocol: other methods for the treatment.Launch-day was defined as day 3-5 of a menstrual cycle, and trigger-day as the day of ovulation triggered with hCG or GnRH agonists.
SPSS 25.0 statistical software was used for analysis.In the study, continuous variables were expressed as mean means ± standard deviation, and compared through Mann-Whitney U test.Categorized data were presented as rate (%), and compared through the Chi-square test.Poisson regression was used for multivariate analysis.A significant difference was considered at P < 0.05.The two groups were balanced using PSM.We used 1:1 match on the nearest neighbor, and the caliper value was 0.05 (Fig. 1).A standardized difference of more than 0.1 indicated that the two groups were well balanced.Adjusted covariates in PSM included number of IVF cycles, ages of the couple, BMI of the female, duration of infertility, type of infertility, infertility diagnoses, ovarian stimulation protocols, basal FSH, basal LH, basal E2, basal AFC, basal CA125, launch-day FSH, launch-day LH, launch-day E2, launch-day AFC, trigger-day LH, trigger-day E2, triggerday P, the number of oocytes, the number of mature oocytes, fertilization method, anesthetic modality.

Results
Before matching, statistically significant differences were found in the characteristics between the two groups, such as POI factor (p = 0.017) and male factor (p = 0.038).After matching, the baseline data between the two groups were not significantly different (P > 0.05).Before matching, the fertilization rate was 77% in the no-anesthesia group, and 76% in the intravenous anesthesia group, without significant between-group difference (P = 0.443).After matching, no difference was observed either (P = 0.685) (Table 1).
According to the results of univariate analyses presented in Table 3, variables including POI, ovarian stimulation protocols (C, E, and G), trigger-day E2, trigger-day P, number of mature follicles, fertilization method, and uterine factor were further examined in multivariable analyses, as shown in Table 4. Statistically significant differences were observed in the impact of ovarian stimulation protocols (C) (b = 0.323, t = 2.421, p = 0.016) and ovarian stimulation protocols (G) (b = 0.073, t = 2.028, p = 0.043) on the fertilization rate, as well as in the impact of the number of mature follicles (b = 0.008, t = 2.380, p = 0.018) and fertilization method (b = 0.063, t = 5.523, p = 0.000) on the fertilization rate (Table 4).The administration of intravenous anesthesia drugs did not demonstrate a significant impact on the rate of fertilized eggs, as indicated by the statistical analysis (b = 0.017, t = 0.813, p = 0.417) presented in Table 3.

Discussion
In clinical practice, an anesthetic modality should be set in subjects according to their willingness, pain tolerance, location of ovary and the number of oocytes.The current study showed that intravenous anesthetic drugs had no impact on the fertilization rate.Additionally considering that intravenous anesthesia could eliminate subjects'   1 Comparison of clinical features before and after matching between the two groups case pain and anxiety, related drugs might be recommended to females receiving oocyte retrieval in IVF.Previous studies have found that the fertilization rate is significantly associated with the pregnancy outcome [6,7].The fertilization rate is a reliable biomarker of oocyte quality.There is also a strong relationship between the fertilization rate and the cumulative live birth rate (CLBR).Rehman et al. [8] have reported that subjects who have a lower fertilization rate achieve poorer pregnancy outcomes.Therefore, fertilization rate is used as a key laboratory indicator for the success or failure of IVF [9].
In this study, the intravenous propofol was used in the anesthesia group.As a popular intravenous drug, propofol functions fast, induces a smooth anesthesia, enables a rapid recovery, and minimizes postoperative events, such as nausea and vomiting.Propofol is also a lipid-soluble substance capable of entering the placenta.Anesthetic neurotoxicity in neonates and young children is a pressing concern [10] A large-scale retrospective study [11] in 2009 has found that children undergoing multiple exposures to anesthesia face an increased risk of neurocognitive defects.It reports that a single exposure to anesthesia before age 4 years is not associated with an increased risk of learning disability (LD), which may be observed in those with more exposures.Some studies [12,13] have reported that chronic and repeated exposure of sedation medication, including benzodiazepines, opioids, propofol, and ketamine, causes neurodegeneration, suggesting that exposures and outcomes may have a dose-response and temporal association.So, repeated and prolonged anesthetic exposure should be avoided in neonates and young children.The present study, for the first time, revealed that after the brief exposure to propofol at the oocyte stage, propofol did not affect the quality of embryos and the IVF pregnancy outcomes.Previous studies have investigated the effects of intravenous anaesthetics on pregnancy.In the studies by Ngamprasertwong et al. [14], an animal model of propofol-induced maternal fetal PK was successfully developed in pregnant sheep for the first time.The concentration of propofol in the fetus was much lower than that in ewes at mid-gestation.A study in the Europe has been conducted to investigate the anesthetics on learning at school age, finding that a brief duration of exposure is not associated with neurodevelopmental disabilities [15,16].Another study has verified that the safety of intravenous anesthetic drugs in cesarean section, suggesting that propofol has no effect on fetal growth and development [17].Two meta-analyses [18,19] have reported intravenous anesthetics, including propofol, fentanyl, and lidocaine, do not affect reproductive outcomes.Indirectly, these observations corroborate the conclusion of the present study.
Notably, oocyte retrieval is anxiety-provoking in the IVF treatment [20].It may take multiple attempts to obtain a pregnancy.Severe pain may cause problems, such as prolonged operation, premature termination, and side effects during surgical procedures.These unpleasant experiences could results in excessive worry about IVF treatment [21] A research of Yoon Frederiksenet al. [22] has shown that about 7% of women feel distressed during oocyte retrieval.Combined with the findings in the present study, anesthetic measures should and could be taken to relieve the pain in women receiving oocyte retrieval.
The innovation of this study is that it adopts PSM to explore the effect of intravenous anesthetic drugs on fertilization rate for the first time.PSM can reduce intergroup differences and balance inter-group confounders.Meanwhile, there are some limitations to the study.First, this study is a single-center retrospective study with a small sample size, which may result in some deviations in the results.Even though PSM was used, unknown residual confounders could not be completely excluded.

Conclusions
Intravenous anesthetic drugs (propofol) might exert no obvious impact on the fertilization rate and pregnancy outcomes in subjects receiving IVF.This finding is worthy of large-size and multi-center studies in the future.

Table 2
Results of the Poisson regression analysis

Table 3
Univariate analyses

Table 4
Multivariable analyses